Assuming you have a seat post and stems that are long enough to put you into the correct riding position, would you go with a larger or a smaller frame? How does the frame size affect your center of gravity? Would the larger or the samller frame be more stable?


I'm asking because I recently rented a bicycle that was 8cm smaller than my current frame. The operator chose the frame size based on 3 measurements that I sent--the height of the saddle relative to the bottom bracket, the distance from saddle to center of handle bars, and the distance from the handlebars to the center of the front axle. Those measurements matched between my home-bike and the rental bike so position-wise, the bikes were identical (albiet the rental had a lot of seat post showing and a high stem). The mechanic that chose the frame size swears that, all things being equal in bike position, one should always choose the smallest frame.

Initially, I found the bike very squirrelly when standing. But, after a few tries, I adjusted. Over the week that I rode it I found that it felt that the bike handled better when descending and on steep grades (20+%) I never had a problem with the front wheel popping up, a problem I have here at home (although the number of steep grades is much smaller)

Now that we're back, I'm wondering if I should seriously be shopping for a bike with a smaller frame. Does the size of the frame, given the same riding position, have that significant a difference in bike control? That is, should I listen to the bike shops and stick with the larger frame or listen to the tour mechanic who swears that one should be on the smallest frame possible?

Some other parameters--I'm big. I stand 6' tall, but I'm almost "normal"-sized in torso and arms. Shops put me on 60cm frames; the tour operator put me on a 52. My home-bike is a Cannondale aluminum with the usual mid-range Shimano parts; the rental was a steel-frame Torrelli with Campy components.

Thanks for any light you can shed on my clouds of confusion.